regulator: tps6105x: add optional devicetree support

Tell the regulator framework to retrieve regulator init
data from the 'regulator' subnode, or from the parent mfd
device's platform data.

Example:

i2c0 {
	tps61052@33 {
		compatible = "ti,tps61052";
		reg = <0x33>;

		regulator {
			regulator-min-microvolt = <5000000>;
			regulator-max-microvolt = <5000000>;
			regulator-always-on;
		};
	};
};

Tree: next-20191118
Signed-off-by: Sven Van Asbroeck <TheSven73@gmail.com>
Link: https://lore.kernel.org/r/20191119154611.29625-3-TheSven73@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>